Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	4 Months Ended	12 Months Ended			88 Months Ended
	Dec. 31, 2012	Aug. 31, 2012	Aug. 31, 2011	Aug. 31, 2010	Dec. 31, 2012
Cash flows from operating activities:
Net loss	$ (19,292)	$ (38,644)	$ (37,195)	$ (18,928)	$ (135,938)
Adjustments to reconcile net loss to net cash used in operating activities:
Employee stock-based compensation expense	2,230	4,487	1,920	217	10,068
Consultant stock-based compensation expense	9	72	197	78	764
Fair value adjustment of common stock warrants	1,484	3,173	16,301	5,895	26,853
Amortization of intangible assets	49	146	153	152	746
Depreciation of fixed assets	42	65	78	72	608
Loss on short-term investments	64	0	0	0	64
Write-off of intangible assets and other intellectual property	0	900	108	0	1,249
Changes in assets and liabilities:
Prepaid expenses and other	1,501	(2,695)	(130)	(79)	(1,370)
Intangible assets				0	(150)
Deposits	79	0	(2)	(3)	(26)
Accounts payable	3,081	754	210	24	4,682
Accrued liabilities	(585)	403	1,119	(2)	1,387
Deferred rent	(8)	(10)	22	3	6
Net cash used in operating activities	(11,346)	(31,349)	(17,219)	(12,571)	(91,057)
Cash flows from investing activities:
Purchase of fixed assets	(55)	(378)	(50)	(20)	(980)
Purchase of short-term investments	(6,853)	(45,307)	0	0	(52,160)
Sale of short-term investments	0	30,000	0	0	30,000
Cash acquired in 2009 Merger				581	581
Change in restricted cash	6	(54)	(114)	0	(163)
Net cash used in investing activities	(6,902)	(15,739)	(164)	561	(22,722)
Cash flows from financing activities:
Proceeds from the sale of common stock	0	42,834	0	19,893	78,504
Proceeds from the sale of common stock under an equity line	0	0	6,740	4,842	11,582
Proceeds from the sale of common stock under an At-the-Market agreement	5,947	7,324	0	0	13,271
Proceeds from the exercise of common stock warrants	1,843	5,013	8,913	475	22,754
Proceeds from the exercise of common stock options	192	366	96	64	727
Proceeds from issuance of note payable	25,000	0	0	0	25,000
Fundraising costs				0	43
Offering costs	25	18	(152)
Debt issuance costs	(1,959)	0	0	0	(1,959)
Proceeds from the sale of common stock to initial investors				0	310
Principal payments on capital lease	(2)	(7)	(5)	(4)	(25)
Net cash provided by financing activities	31,046	55,548	15,592	25,270	150,207
Effect of exchange rates on cash and cash equivalents	(65)	(52)	10	(8)	(115)
Net increase (decrease) in cash and cash equivalents	12,733	8,408	(1,781)	13,252	36,313
Cash and cash equivalents, beginning of period	23,580	15,172	16,954	3,702	0
Cash and cash equivalents, end of period	36,313	23,580	15,172	16,954	36,313
Supplemental cash flow information:
Interest Paid	83	3	2	4	100
Supplemental disclosure of non-cash financing activities:
Warrants issued in connection with financings				9,677	16,310
Initial fair value of warrants issued to placement agents in connection with financings				209	209
Common stock and warrants issued in connection with reverse merger				4,417	4,417
Common stock issued as fee for equity line	0	0	519	309	828
Acquisition of equipment in exchange for capital lease	0	13	14	0	48
Fair value of warrant liability reclassified to equity upon exercise	2,345	9,482	8,506	0	20,333
Notes receivable issued in exchange for common stock				0	110
Common stock issued for a finder's fee				0	102
Common stock issued in asset purchase				$ 0	$ 2,899